title: Oxygen-dependent 1,25-dihydroxycholecalciferol-induced calcium ion transport in rat intestine.
abstract: O2-dependent CA2+ uptake by rat duodenal discs has been characterized and used in a revised assay for 1,25-dihydroxycholecalciferol-induced intestinal Ca2+ transport. Although both muscle and mucosal surfaces are exposed in this free-floating-disc assay, the Ca2+ influx across the muscle surface is small, not O2- or vitamin D-dependent, and can be subtracted out. Depriving the animals of food for 9-14 h before assay increases the O2-dependent uptake by about 75%. Half-saturation values for O2-dependent Ca2+ uptake as determined with this assay are: 0.8mM-Ca2+ (fed) and 0.5mM-Ca2+ (food-deprived) for vitamin D-deficient rats, and 0.9mM-Ca2+ (fed) and 1.5mM-Ca2+ (food-deprived) for rats dosed with 1,25-dihydroxycholecalciferol. The maximum velocity of uptake varies from 6.7nmol of Ca2+ per cm2/min (fed) to 7.0nmol of Ca2+ per cm2/min (food-deprived) for vitamin D-deficient rats and 16.7nmol of Ca2+ per cm2/min (fed) to 29 nmol of Ca2+ per cm2/min (food-deprived) for 1,25-dihydroxycholecalciferol-treated rats. By using a 5 min preincubation and 15 min incubation with 1.0mM-Ca2+, duodenal tissue taken from vitamin D-treated rats shows about a 3-fold increase in O2-dependent Ca2+ uptake when compared with tissue taken from vitamin D-deficient animals. The calcium ionophore A23187, depending on concentration, either has no significant effect on or inhibits the O2-dependent uptake, rather than increasing it. Actinomycin D, at a dose of 2 micrograms/g, inhibits the O2-dependent uptake in intestinal discs from both vitamin D-deficient and vitamin D-treated rats by 58 and 80% respectively, when administered in vivo 3 1/2 h before assay.
mesh_terms: D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D000001:Calcimycin / Q000494:pharmacology; D002117:Calcitriol / Q000494:pharmacology*; D002118:Calcium / Q000378:metabolism*; D003609:Dactinomycin / Q000494:pharmacology; D004386:Duodenum / Q000187:drug effects / Q000378:metabolism*; D066298:In Vitro Techniques; D007413:Intestinal Mucosa / Q000378:metabolism; D008297:Male; D010100:Oxygen / Q000378:metabolism*; D051381:Rats
chemical_list: D003609:Dactinomycin; D000001:Calcimycin; D002117:Calcitriol; D010100:Oxygen; D002118:Calcium